Small particles (particulate phase) embedded within and having a different refractive index (η) than a continuous phase or matrix can cause light passing through the continuous phase to scatter. Milk is a common example of this phenomenon. However, if the indices of refraction of the particles and continuous phase approximately equal, the entire medium appears to be transparent. More specifically, the amount of light scattering in such a medium depends upon the contrast in (η) between the two phases, the size distribution and concentration of the particles, and the thickness (optical path) of the medium.
Murase et al. (Macromolecules 1997, 30, 8088-8090) describe creating a change in refractive index by photodimerization of poly(vinyl cinnamate) films.
U.S. Pat. No. 6,569,600 (Dinnocenzo et al.) describes optical recording materials that when exposed to actinic radiation, produce a change in optical properties in the exposed regions, thereby providing an image or stored data. These results can be achieved by using organic materials that are altered by exposure to actinic radiation and through one electron oxidation, cause the desired change in optical properties. Such organic materials can be changed by isomerization reaction such as cyclizations, cycloadditions, and cycloreversions, and are disposed within a suitable organic polymeric matrix. The changes in optical properties are useful for recording holograms, diffraction gratings, and waveguides. There is no indication that the index of refraction of the organic materials should be chosen with a specific relationship to the index of refraction of the polymeric continuous phase.
Problem to be Solved
There is a need for improved imaging media that can utilize known reactive chemicals in a more efficient manner and in which the image is controlled by effective use of differential light scattering by various components in the imaging composition.